The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is a pest of rice in the seven rice producing states of the United States and several countries where it has been introduced. Carbofuran was used adequately for nearly 30 yr, but it is no longer registered for use in rice and has been replaced by λ-cyhalothrin (Karate) and diflubenzuron (Dimilin). The scouting methods for carbofuran were inadequate or too late in determining the need for insecticide applications of the newer insecticides. Therefore, a new population monitoring method was developed using a double-ended aquatic barrier trap. The trap function was based on weevil swimming behavior, and 16 barrier trap prototypes were tested on adult weevils, 22–23 July 1998, in a small bay of late planted rice. Adult means ± SE were 73.9 ± 9.4 per trap on 23 July 1998 and 54.4 ± 6.4 per trap on 24 July 1998. The core sample mean for this plot was 72.9 ± 7.0 larvae per core. The trap was tested in both commercial fields and early and late planted small bays in 1999. Larval weevil infestations ranged from moderate (near or slightly below the economic injury level (EIL) to high (62.8 per core). Regression analyses showed a significant correlation between adults captured in traps to subsequent larval density in field edges (r² = 0.98) and field interiors (r² = 0.92). For every 1.0 rice water weevil adult captured in barrier traps, a density of 1.2–2.8 larvae per core sample was predicted. The aquatic barrier traps caught adult weevils without lures. Trapping rice water weevil adults immediately after permanent flood in drill-seeded fields can be used to aid decision making for insecticide application in rice.